We detail the forward and backward blackmessage passing in each subgraph of the factor graph in Fig. REF  according to the principle of SVMP [1]}, [2]}, [3]}. blackThe notation \(\mathcal {M}_{n_a \rightarrow n_b} (x)\)  is used to denote a message passed from node \(n_a\)  to node \(n_b\) , which is a function of \(x\) . blackNote that, if a forward message computation requires backward messages, we use the
messages in previous iteration by default.
